private static ConstraintParseResults ParseConstraints(
string text,
string parameterName,
int currentIndex,
int endIndex)
{
var constraints = new List <RoutePatternConstraintReference>();
var state = ParseState.Start;
var startIndex = currentIndex;
do
{
var currentChar = currentIndex > endIndex ? null : (char?)text[currentIndex];
switch (state)
{
case ParseState.Start:
switch (currentChar)
{
case null:
state = ParseState.End;
break;
case ':':
state = ParseState.ParsingName;
startIndex = currentIndex + 1;
break;
case '(':
state = ParseState.InsideParenthesis;
break;
case '=':
state = ParseState.End;
currentIndex--;
break;
}
break;
case ParseState.InsideParenthesis:
switch (currentChar)
{
case null:
state = ParseState.End;
var constraintText = text.Substring(startIndex, currentIndex - startIndex);
constraints.Add(RoutePatternFactory.Constraint(constraintText));
break;
case ')':
// Only consume a ')' token if
// (a) it is the last token
// (b) the next character is the start of the new constraint ':'
// (c) the next character is the start of the default value.
var nextChar = currentIndex + 1 > endIndex ? null : (char?)text[currentIndex + 1];
switch (nextChar)
{
case null:
state = ParseState.End;
constraintText = text.Substring(startIndex, currentIndex - startIndex + 1);
constraints.Add(RoutePatternFactory.Constraint(constraintText));
break;
case ':':
state = ParseState.Start;
constraintText = text.Substring(startIndex, currentIndex - startIndex + 1);
constraints.Add(RoutePatternFactory.Constraint(constraintText));
startIndex = currentIndex + 1;
break;
case '=':
state = ParseState.End;
constraintText = text.Substring(startIndex, currentIndex - startIndex + 1);
constraints.Add(RoutePatternFactory.Constraint(constraintText));
break;
}
break;
case ':':
case '=':
// In the original implementation, the Regex would've backtracked if it encountered an
// unbalanced opening bracket followed by (not necessarily immediatiely) a delimiter.
// Simply verifying that the parantheses will eventually be closed should suffice to
// determine if the terminator needs to be consumed as part of the current constraint
// specification.
var indexOfClosingParantheses = text.IndexOf(')', currentIndex + 1);
if (indexOfClosingParantheses == -1)
{
constraintText = text.Substring(startIndex, currentIndex - startIndex);
constraints.Add(RoutePatternFactory.Constraint(constraintText));
if (currentChar == ':')
{
state = ParseState.ParsingName;
startIndex = currentIndex + 1;
}
else
{
state = ParseState.End;
currentIndex--;
}
}
else
{
currentIndex = indexOfClosingParantheses;
}
break;
}
break;
case ParseState.ParsingName:
switch (currentChar)
{
case null:
state = ParseState.End;
var constraintText = text.Substring(startIndex, currentIndex - startIndex);
if (constraintText.Length > 0)
{
constraints.Add(RoutePatternFactory.Constraint(constraintText));
}
break;
case ':':
constraintText = text.Substring(startIndex, currentIndex - startIndex);
if (constraintText.Length > 0)
{
constraints.Add(RoutePatternFactory.Constraint(constraintText));
}
startIndex = currentIndex + 1;
break;
case '(':
state = ParseState.InsideParenthesis;
break;
case '=':
state = ParseState.End;
constraintText = text.Substring(startIndex, currentIndex - startIndex);
if (constraintText.Length > 0)
{
constraints.Add(RoutePatternFactory.Constraint(constraintText));
}
currentIndex--;
break;
}
break;
}
currentIndex++;
} while (state != ParseState.End);
return(new ConstraintParseResults(currentIndex, constraints));
}